1. Field of the Invention
This invention generally relates to an input peripheral device, and more particularly to a touch pad and a position detecting circuit and method thereof.
2. Description of Related Art
As the technology advances, the computer hardware and software are being well developed. Among those hardware and software developments, the development of the children educational hardware and software is one of the most important fields. To facilitate the childrens operating the children educational hardware and software, the touch pad generally is used as the input peripheral device.
FIG. 1 is the simplified diagram of a touch pad. Referring to FIG. 1, the touch pad includes a sensing pad 110, a sensing pen 120 and a position detecting circuit (not shown). The sensing pad 110 has points A and B in the vertical direction and points C and D in the horizontal direction for receiving the input signals. Because the sensing pad 110 is uniformly resistance-distributed, the electrical field generated by the input signals will be uniformly distributed. Hence, the position detecting circuit can detect the position of the sensing pen 120 based on the sensing signal detected by the sensing pen 120.
FIG. 2 is the waveform of the touch pad oF FIG. 1 during the input operation. Referring to FIG. 2, during the stage S1, the same voltage will be applied to points A, B, C, and D. Hence, the sensing signal detected by the sensing pen 120 is shown as the waveform E during the stage S1. The magnitude of waveform E will be used for determining the position of the sensing pen 120 during the stages S2 and S3. As shown in FIG. 2, during the stage S2, the same voltage as in the stage S1 will be applied to point A only; during the stage S3, the same voltage as in the stage S1 will be applied to point C only. Because the sensing pad 110 is uniformly resistance-distributed, the waveform E detected by the sensing pen 120 during the stages S2 and S3 is shown in FIG. 2. The position detecting circuit will depend on the ratio of the magnitude of the waveform E during the stages S2 and S3 to the magnitude of the waveform E during the stage S1 to determine the position of the sensing pen 120.
However, the prior art has the following drawbacks: 1. Because it uses the magnitude of the sensing signal detected by the sensing pen to determine the position of the sensing pen, it requires a higher resolution, which means that it requires more precise analog-to-digital converters and therefore it is hard to reduce the cost. 2. It is hard to control the preciseness and the specification for mass production by detecting the magnitude or energy of the induced voltage.